[Intel-gfx] [PATCH] drm/i915/execlists: Use a local lock for dfs_link access

[Daniel Vetter]

On Wed, Nov 16, 2016 at 04:03:27PM +0000, Chris Wilson wrote:
> On Wed, Nov 16, 2016 at 03:54:23PM +0000, Tvrtko Ursulin wrote:
> > 
> > On 16/11/2016 15:27, Chris Wilson wrote:
> > >Avoid requiring struct_mutex for exclusive access to the temporary
> > >dfs_link inside the i915_dependency as not all callers may want to touch
> > >struct_mutex. So rather than force them to take a highly contended
> > >lock, introduce a local lock for the execlists schedule operation.
> > >
> > >Reported-by: David Weinehall <david.weinehall at linux.intel.com>
> > >Fixes: 9a151987d709 ("drm/i915: Add execution priority boosting for mmioflips")
> > 
> > Grumble grumble, sloppy review. :I
> 
> Too busy living the good life with working atomic flips.
>  
> > >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > >Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > >Cc: David Weinehall <david.weinehall at linux.intel.com>
> > >---
> > > drivers/gpu/drm/i915/intel_lrc.c | 7 +++++--
> > > 1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > >diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> > >index e23b6a2600fb..10e59ff0d8f1 100644
> > >--- a/drivers/gpu/drm/i915/intel_lrc.c
> > >+++ b/drivers/gpu/drm/i915/intel_lrc.c
> > >@@ -694,6 +694,7 @@ pt_lock_engine(struct i915_priotree *pt, struct intel_engine_cs *locked)
> > >
> > > static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
> > > {
> > >+	static DEFINE_MUTEX(lock);
> > 
> > Good enough for one GPU. :) Consider improving in the future as it
> > is not in the spirit of the driver.
> 
> Actually... Being able to PI across multiple GPUs is part of the dream.
> In that case, it does need to be a global lock - just a bit iffy on
> getting dependency tracking into a common layer.

Why exactly does this need a global lock? And yes static mutex in a
function looks evil, pls move right next to the data.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch